1. Field of the Invention
The present invention relates to a ceramide-like compound having properties of the natural ceramides, and to a method for producing the same, and to a cosmetic composition containing the same as a active ingredient.
2. Related Arts
An organism needs protective barrier which prevents noxious foreign materials including microorganisms from external penetration, and counteracts the loss of body fluids such as water and blood, to maintain its life action. In case of human being, stratum corneum, the outermost layer of the epidermis, serves as this protective barrier. The stratum corneum prevents water within the skin from excessive evaporation, and controls penetration of foreign materials.
Dead, flat-shaped cells, corneocytes filled with keratin are embedded in the lipids of the intercellular domains to form membraneous bilayers. The corneocytes and the intercellular lipids make up the so-called permeable barrier. The intercellular space of the stratum corneum is mainly composed of glycolipids, cholesterol, free fatty acids and ceramides. Among them, the ceramides play an important role in maintaining well-balanced water content which is involved in skin elasticity, appearance and barrier functions.
The ceramides detected in human stratum corneum, which are represented by the following Formulae 3 to 9, contain sphingosine represented by the Formula 1 or phytosphingosine represented by the Formula 2 in the structure. ##STR1##
However, skin aging or skin damage caused by detergents which remove the lipids essential for the barrier function may disturb lipid synthesis and reduce ceramide content in the stratum corneum. Thus, cell cohesion may be weak and the stratum corneum cannot serve as a protective barrier. The skin may lose elasticity. As the ceramide content decreases, transepidermal water loss, direct exposure to the exterior irritation such as UV or chemicals, and peeling off of the stratum corneum may occur and thus the skin may be rough and damaged.
It has been reported that external application, such as cosmetics or pharmaceutical application, of ceramides can recover the lamella structure disturbed by skin aging or damage of the stratum corneum. Thus, stratum corneum can fully function as a protective barrier.
For the purpose of external application of ceramides, efforts have been made to find natural ceramides in animals, plants and microorganisms. As a result, various animals, plants and microorganisms containing natural ceramides were discovered. However, ceramide content of natural origin is very low. And it is difficult to isolate highly pure ceramides. Thus, supplies of natural ceramides by extraction thereof increase manufacturing cost and the price of final product. In addition, natural ceramides have low solubility in various organic solvents widely used in the cosmetics. That is to say, only small quantity of ceramides can be used in the cosmetics, which hinders providing their sufficient primary effects.
The present inventors have conducted extensive studies for the molecular structure of natural ceramides, in order to synthesize ceramide-like compounds which are structurally similar to natural ones. Natural ceramides have two long chain alkyl groups, amides, and hydroxyl groups. Considering this structural feature, molecular design was performed to synthesize ceramide-like compounds having two long chain alkyl groups, one or more amides and hydroxyl groups, and confirmed effectiveness in skin tonicity and recuperation after the composition containing the compound of the present invention had been applied onto the skin.
Skin ceramides form a stable lamella layer in the stratum corneum for their function as the skin barrier. Thus ceramide-like compounds should be also easily delivered into the intercellular space of the stratum corneum. Under this consideration, the present inventors introduced phosphoric or sulfuric group into the ceramide-like structures. The phosphoric or sulfuric group enhance the penetration through the skin surface. They are removed easily by enzymes, and then transformed into more stable lipophilic form.